Effects of DDT on electrical properties of lecithin-decane bilayer membranes

Lecithin-decane bilayer membranes were treated with DDT and valinomycin, either by adding the compounds to the electrolyte around the membrane or by adding them directly to the lecithin-decane. Membrane capacitance was calculated using the dc transient technique. Specific capacitance was determined from capacitance versus area regressions and was not significantly altered by DDT. Specific K⁺ conductance was decreased by DDT, but only when DDT and the K⁺ carrier, valinomycin, were administered to the electrolyte where they may have interacted hydrophobically. It is concluded that the valinomycin-induced conductance of artificial membranes is inappropriate as a model for investigating the effects of DDT on the electrical properties of excitable membranes.     

Effects of DDT on the cockroach nervous system at three temperatures

Some effects of DDT on the cockroach nervous system have been correlated with poisoning symptoms, using free-walking cockroaches with implanted electrodes. Experiments at 16.5°C and 32°C used LD₉₅ doses and at 25°C, an estimated LD₉₅. DDT had excitant actions on each nerve studied; cercal afferent and efferent neurones, and abdominal interneurones. The effects on the central nervous system became more marked as temperature was reduced, despite the smaller quantity of DDT employed, but the excitant actions on the peripheral nervous system were not quantified. It is suggested that the effects of DDT on the cockroach nervous system could account for the negative temperature coefficient of toxicity of DDT.     

Effects of DDT on labellar receptors in two DDT-resistant and two DDT-susceptible strains of house flies

Electrophysiological responses of labellar hairs of resistant and susceptible strains of the house fly were recorded at times following treatment of the hairs with DDT. Under the influence of DDT, the receptors of a hair discharged groups of impulses in high-frequency trains instead of the usual regular volley. The effect was observed to gradually spread to nontreated hairs. Among four strains chosen for gradation from high resistance to high susceptibility, in general the relative effectiveness of DDT corresponded to overall resistance as indicated by LD₅₀ data. The highly resistant strain showed essentially no effects, and the other strains showed effects with some degree of recovery. Results for the highly susceptible strain were anomalous in not differing significantly from those of the moderately resistant strai. Unexpectedly small effects in the highly susceptible strain point to a strain characteristic not necessarily correlated with LD₅₀ data.     

Residues of DDT in cottonseed after spraying with DDT and torbidan

DDT at 1.12 and 2.24 kg/ha a.i. and Torbidan at 5 and 10 litre formulation/ha (1 and 2 kg DDT/ha) were sprayed five times on cotton over a period of 15 weeks. Seeds from the first pick of the crop were found to contain as residues pp′-DDT and pp′-DDE [1,1-dichloro-2,2-di- (4-chlorophenyl)ethylene]. The highest residue level (0.783 parts/10⁶) was found in seeds from Torbidan 10 litre/ha treatment.     

不同密度与施氮量对干旱区玉米产量及其构成因素的影响研究

为确定甘肃中部干旱区玉米种植的最佳密度和施氮量,采用田间试验方法,选用适宜性玉米新品种福地201和高玉811为试验材料,研究了不同密度与不同施氮量对其产量及产量构成性状的影响,分析其产量表现及综合性状以确定最佳增产配方,为提高甘肃中部旱作农业区全膜双垄沟播玉米增产潜力提供理论支持。结果表明:(1)在全膜双垄沟播栽培技术条件下,通过分析密度和施氮量对玉米产量相关因素关系的影响得出,高产稳产最佳种植密度为7.2万株·hm~(-2),施氮量675 kg·hm~(-2),果穗干物质产量达13 792.35 kg·hm~(-2);(2)产量随施氮量增加明显,茎粗则随追氮肥量增加先缓增后明显下降;(3)密度增加,产量下降不明显,但茎粗减小极显著,抗倒性降低,稳产性减弱,低密度增施氮肥,增产效果明显;(4)不同密度与施氮量处理下各性状与产量相关系数达到0.7977,通过0.001信度检验,达到极显著相关水平。     

Effect of DDT on photosynthesis of Selanastrum capricormutum

The effect of DDT (2,2-bis-(p-chlorophenyl)-1,1,1-trichloroethane) on carbon assimilation of a green alga, Selanastrum capricormutum was studied. DDT at concentrations between 3.6 and 36 ppb was inhibitory to the photosynthetic CO₂ fixation (ethanol-soluble and/or ethanol-insoluble) and the longer the exposure to DDT, the greater the inhibition. Kinetic studies of photosynthetic CO₂ fixation indicated that DDT stimulated the incorporation of carbon-14 into glycolic acid, a major compound of photorespiration and caused the concomittant suppression of flow of carbon-14 into aspartic acid, a major component of the C₄-dicarboxylic acid pathway. The shift from an efficient pathway into a nonefficient pathway by DDT was interpreted to be through interruption of cyclic photophosphorylation.     

夏播大豆田秸秆覆盖对杂草发生的影响与减量用药研究

2008年和2009年调查了旋耕和秸秆覆盖条件下夏播大豆田杂草的发生规律和对大豆出苗的影响。播后21 d内杂草出土量占大豆整个生育期杂草出土量的79.3%~96.5%,是化学防除的关键时期。降雨是影响田间杂草发生的重要因素。4 500 kg/hm2的秸秆覆盖对田间杂草有48.67%~79.90%的抑制效果,可减轻大豆播种后因干旱对出苗的影响。秸秆覆盖后可减少精喹禾灵用量33%。     

氧硫化碳熏蒸处理对苹果贮藏品质的影响

氧硫化碳作为一种新型环保的溴甲烷替代熏蒸剂,在水果检疫处理中可能有着广泛的应用前景.本文探讨了25℃条件下不同剂量氧硫化碳熏蒸处理对苹果主要贮藏品质指标的影响.结果表明,处理组苹果呼吸作用在熏蒸过程被显著增强,却在储藏期间被抑制;熏蒸处理对储藏期苹果的失重有显著的抑制作用;熏蒸处理对储藏期苹果的硬度、可溶性糖和总酸度均无明显影响;90 g/m3的氧硫化碳熏蒸4h,苹果表皮无药害.     

不同清洗和储藏方式下戊唑醇在黄瓜中的残留变化

以田间施药后的黄瓜为研究对象,模拟家庭清洗和储藏方式,利用液相色谱串联三重四级杆质谱(ultra performance liquid chromatography coupled with tandem mass spectrometry,UPLC-MS/MS)对不同清洗和储藏方式下黄瓜中的戊唑醇残留进行测定,旨在探究从田间到餐桌,鲜食黄瓜时农药残留的去除方法,为膳食风险评估提供理论参考。结果表明,在不同的清洗方式下清洗15 min后,黄瓜中戊唑醇的去除率达到31.82%~78.79%。其中5%乙酸溶液对戊唑醇去除效果最佳。室温22℃时放置48h戊唑醇去除率达到67.42%。超声波清洗15min后戊唑醇的去除率为76.51%。     

Mechanism of DDT resistance in larvae of the mosquito Aedes aegypti L.; The effect of DDT selection

Selection with pp'-DDT was applied to fourth-stage larvae of Aedes aegypti along four lines, starting with larvae of the F₂ generation from crosses between a susceptible strain and each of four resistant strains (two of Trinidad origin and two of Bangkok origin). Larval resistance increased substantially along each line but there was little or no change in the percentage breakdown of DDT to 1,1-dichloro-2,2-bis(4-chloro-phenyl)ethylene (pp'-DDE) in vivo and in no line were these two variables significantly correlated. Percentage breakdown was generally higher at 10 mg than at 50 mg litre^?1. DDT uptake (defined as content of DDT+pp'-DDE) was generally higher after exposure to 50 mg than to 10 mg litre^?1. It increased significantly with selection in the TE×NS line; it remained unchanged in the T8 × NS line; and in the other two lines (BSJ × NS and B51 × NS), it increased initially but dropped as selection progressed, the reduction being highly significant in the second of these lines. The amount of internal residual (unmetabolised) DDT tolerated by larvae of the TE × NS line also increased significantly with resistance. The levels in the other lines followed the pattern of uptake, remaining steady in T8 × NS despite the increase in survival, rising at first and then declining in the two Bangkok lines. Thus selection produced a higher tolerance to internal unmetabolised DDT in the two Trinidad lines but led ultimately to a lower content of DDT+pp'-DDE in the two Bangkok lines. The reasons for this behaviour are discussed.     

秋覆盖的保水效应及对春玉米生长的影响

设置高(9000 kg·hm^-2)、中(6000 kg·hm^-2)、低(3000 kg·hm^-2)3种不同量秸秆覆盖和平覆、垄覆2种不同方式的地膜覆盖,以全程不覆盖为对照,研究了秋季雨后覆盖(休闲期加生育期全程覆盖)对土壤水分及春玉米生长状况的影响。结果表明：在冬闲期,各覆盖处理(除秸秆覆盖3 000 kg·hm^-2处理)的土壤蓄水量分别较不覆盖处理(CK)增加了21.22 mm、20.49 mm、18.37mm和19.5mm,使玉米出苗较CK至少提前了3 d。在播种期~大喇叭口期(播后70 d),平覆地膜和垄覆地膜平均土壤蓄水量分别较对照增加15.57 mm和15.73 mm;秸秆覆盖6 000 kg·hm^-2和9 000 kg hm^-2处理平均土壤蓄水量分别较对照增加12.05 mm和12.03 mm。秸秆覆盖处理在玉米生长后期土壤蓄水量较对照增加不显著。秋覆盖处理均可促进春玉米个体的生长,地膜覆盖处理可以显著提高春玉米生长前期的单株干重、株高和叶面积,秸秆覆盖在生育后期较对照显著提高。平覆地膜、垄覆地膜两个处理的玉米籽粒产量和水分生产效率分别较对照增加14.6%、13.9%和11.0%、11.1%(P<0.05),秸秆覆盖处理增产均不显著。     

Distribution and breakdown of DDT in orchard soil

Amounts of DDT and its breakdown products were determined in soil in an apple orchard in Herefordshire. Samples were taken for a number of years (1972–79) after use of the insecticide in the orchard had ceased in 1969. The results were compared with those obtained in an investigation of the same orchard in 1968. From 1968 to 1979, soil residues of pp′-DDT, p′--DDT and pp′--TDE decreased gradually whereas those of pp′--DDE increased, and there were linear relationships between log (concentration) and time. The calculated time for 50% decrease in concentration (Dt₅₀) was 11.7 years for pp′--DDT, 3.3 years for pp′--TDE and 7.1 years for op′--DDT; the time for doubling the concentration for pp′--DDE was 9.1 years. Regression analysis on the two major components (pp′--DDT+pp′--DDE) indicated that the total amount (2.7 mg kg^?1) was not decreasing with time. It was concluded that during a post-spray era, the breakdown of pp′--DDT to pp′--DDE was a significant feature of the persistence of DDT, and that, in contrast to the findings of other workers who sampled when DDT was being used, there were no losses by volatilisation. There was an exponential decrease in the amount of DDT residues with increasing soil depth and approximately 90% was found in the top 10 cm of the undisturbed soil profile.     

黄土地表生物结皮对土壤贮水性能及水分入渗特征的影响

采用双环法对山西省偏关县3种结皮覆盖下(苔藓藻结皮、藻结皮和薄层藻结皮)土壤的贮水性能和渗透特征进行了对比研究.结果表明:不同结皮覆盖下土壤的贮水能力受结皮厚度和孔隙度状况的影响较大,0～10 cm土层饱和贮水量为502.69～525.80 t/hm2 ,滞留贮水量为169.71～198.29 t/hm2;初渗速率的变化范围为5. 19～11.10 mm/min,无结皮最高,苔藓藻结皮最低;稳渗速率变化范围为1.6 7～2.67 mm/min.采用的3种入渗模型(Kostiakov模型、Horton模型和Ph ilip模型)中Horton模型的拟合值更接近于实测值, 决定系数R2在0.98～0.99,更适用于描述本研究区具有生物结皮土壤的入渗特征.     

Differential inhibition responses caused by DDT on oligomycin-sensitive Mg2+-ATPase activity: Nature of the requirements for DDT sensitivity

Earlier communications from this laboratory have shown that DDT inhibited oligomycin-sensitive Mg²⁺-ATPase (EC 3.6.1.3) but that its active component, F₁, was not affected. In the present investigation evidence has been obtained to determine the nature of the requirements for DDT sensitivity. The results showed that DDT sensitivity was conferred to F₁ from pig heart mitochondrial preparations when it was bound to F₀ from the same preparation. The F₁ from house fly (Musca domestica L) thorax was able to bind to F₀ from pig heart. This combination showed similar sensitivity to that of the original F₁-F₀ combination from pig heart mitochondria. However, when F₁ from pig heart mitochondria was incorporated into F₀ depleted in oligomycin sensitivity-conferring protein (OSCP) from the same source, the resulting ATPase activity was insensitive to DDT. Addition of crude (50–200 μg) or purified (5–20 μg) OSCP in the above preparation restored DDT sensitivity. Presence of dioleyl or dipalmitoyl phosphatidyl choline or Triton X-100 in the reaction medium antagonized the DDT inhibitions. Depletion of phospholipids from submitochondrial membrane preparations (SMP) decreased ATPase activity. Addition of dioleyl or soybean phosphatidyl choline to this lipid-depleted preparation restored DDT sensitivity. Evidence presented suggests that DDT acted on F₁ in association with one or more membrane components and that OSCP and phospholipid were essential for DDT sensitivity.     

The effects of DDT and dieldrin on rat peritoneal macrophages

The effects of DDT and dieldrin on cell population, viability, and phagocytic activity on the rat peritoneal macrophages were studied. It was observed that both pesticides, at low levels of concentration, exhibited a marked effect on this cell type. At the lowest concentrations tested both pesticides produced an increase in the macrophage population which appeared to be the result of a foreign-body response. At higher concentrations of pesticide this foreign-body response appears to be inhibited. The phagocytic activity of the cells steadily decreased as the concentration of the pesticide administered increased, and a decrease in cell viability with increased pesticide exposure was also noted.     

Effects of landscape fragmentation of plantation forests on carbon storage in the Loess Plateau,China

Tree plantation and forest restoration are the major strategies for enhancing terrestrial carbon sequestration and mitigating climate change. The Grain for Green Project in China has positively impacted global carbon sequestration and the trend towards fragmentation of plantation forests. Limited studies have been conducted on changes in plantation biomass and stand structure caused by fragmentation, and the effect of fragmentation on the carbon storage of plantation forests remains unclear. Thi...     

喷施不同钙肥对苹果贮藏期间抗氧化酶活性的影响

以“天富一号”苹果为试材,探讨了钙肥对贮藏期间果实抗氧化酶活性的影响,结果表明:在0℃贮藏条件下红富士果肉SOD、CAT高峰出现的时间一致,表明SOD、CAT是协同作用的,它们是果实贮藏前期的主要作用酶,共同防御活性氧或其过氧化物自由基对细胞膜系统的伤害.贮藏60 d后POD活性显著增加,MDA含量在贮藏后期也逐渐增加,表明POD是贮藏后期的主要作用酶.喷施不同钙肥均能显著提高SOD、CAT的活性,降低了MDA含量,其中功能性叶面肥作用效果优于营养型叶面肥,螯合氨基酸钙处理下SOD、CAT含量最高,其次为早地龙腐殖酸,因此可选择螯合氨基酸作为延长苹果贮藏期的最佳钙肥,旱地龙腐殖酸因其具有抗旱能力可适用于干旱地区果园.     

秸秆还田下减量施氮对作物产量及养分吸收利用的影响

秸秆还田条件下,采用多年田间定位试验研究了N肥减量施用对作物产量、养分吸收利用以及土壤表观N平衡的影响,旨在为关中小麦／玉米一年二熟轮作区合理施用N肥提供依据。结果表明：与常规施N处理（玉米季施氮187．5 kg·hm－2,小麦季施氮150 kg·hm－2）相比,2008—2011年三年中,15％减N、30％减N两个处理均未显著降低作物籽粒与秸秆产量;2010—2011年生长季中,15％减N处理降低了作物秸秆N、P、K周年总吸收量,增加了籽粒N、P、K周年总吸收量,其中籽粒P周年总吸收量增加达显著性水平;30％减N处理显著降低了籽粒N和秸秆N、K周年总吸收量,降幅分别为12．9％、41．9％、18．5％,在小麦收获后,30％减N处理的N素盈余量只有11．3 kg·hm－2,有潜在缺N危险。综合考虑产量、养分吸收利用及土壤表观N平衡,在秸秆还田条件下,15％减N处理的施N量（即玉米季施氮159 kg·hm－2,小麦季施氮127．5 kg·hm－2）为本地区最佳N肥用量。